Measured reflectance spectra of the four PLCCO samples at various temperatures can be found in Supplementary Information. We compared the measured reflectance spectra of PLCCO with those of electron-doped NCCO [1]}, [2]} and PCCO [3]}, [4]}, and hole-doped LSCO [5]} previously reported in literature. We display the measured reflectance spectra of the four PLCCO samples at 300 K in Figure 1(a). We observe a linear frequency dependence of reflectance spectra (also see Fig. 2(c) and (d)) in a wide spectral range for the optimally doped and overdoped samples, which is suggestive of a marginal Fermi liquid response [6]}, [7]}. The plasma edge appears as a dip near 8000 cm\(^{-1}\) . We note that the plasma edge of the as-grown sample is less well-defined, which may be related to the ARPES observation that the Fermi surface of this sample is not well-defined [8]}. The concentration-dependent (or heat-treatment-dependent) reflectance change can be clearly seen in Fig. 1(a). The reflectance in the mid-infrared (MIR) region below 6000 cm\(^{-1}\)  increases with the concentration, which is a common doping-dependent behavior in cuprate systems. However, the magnitude of the doping-dependent reflectance change is much smaller than those of other electron-doped cuprates as observed in Fig. 1(b). This can be associated with the widest superconducting dome of PLCCO among the electron-dope families [9]}. To further study the different doping-dependent reflectance changes, we display the reflectance spectra of electron-doped NCCO [2]} and hole-doped LSCO [5]} at various doping levels at \(T\)  = 300 K in Fig. 1(b) and 1(c), respectively, along with the reflectance of our PLCCO sample with \(n\)  = 0.14 at the same temperature. In Fig. 1(b), the reflectance of PLCCO at \(n\)  = 0.14 is lower than that of NCCO at \(x\)  = 0.095. We can see also that the doping-dependent reflectance change in NCCO is much larger than that in PLCCO. The plasma edge of PLCCO (\(\sim \) 8000 cm\(^{-1}\) ) is lower than those of NCCO (9000 - 11,000 cm\(^{-1}\) ).
